1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing a semiconductor device, and more particularly to a semiconductor device that includes a porosified insulating film and has a multilevel interconnect structure based on a damascene structure and a method for manufacturing the same.
2. Description of the Related Art
In step with miniaturization and increase in the integration degree of semiconductor devices, delay of electrical signals attributed to the time constant of interconnects is increasingly becoming a serious problem. To address this, for conductive layers in a multilevel interconnect structure, use of copper (Cu) interconnects, which have low resistivity, has been advanced instead of use of aluminum (Al) alloy interconnects. The Cu however is difficult to pattern by dry etching unlike metal materials such as Al used in existing multilevel interconnect structures. Therefore, typically multilevel Cu interconnect structures employ a damascene method, in which interconnect trenches are formed in insulating films and a Cu film is buried in the interconnect trenches. In particular, a dual damascene method is attracting attention. In this method, after formation of connection holes and interconnect trenches, Cu is buried in the holes and trenches simultaneously. The dual damascene method therefore is advantageous for reducing the number of steps.
In highly-integrated semiconductor devices, increase in the capacitance between interconnects causes the lowering of the operation speed of the semiconductor devices. Therefore, for such semiconductor devices, minute multilevel interconnects are used for which low dielectric constant materials are used as interlayer insulating films to thereby suppress the increase in the capacitance between interconnects. Examples of the material of the low dielectric constant interlayer insulating film include, in addition to a fluorine-doped silicon oxide (FSG), which is a comparatively proven material having a dielectric constant of about 3.5, low dielectric constant materials having a dielectric constant of about 2.7 such as organic polymers typified by polyarylether (PAE) and inorganic materials typified by hydrogen silsesquioxane (HSQ) and methylsilsesquioxane (MSQ). Furthermore, in recent years, use of low dielectric constant materials that arise from porosification of these materials and have a dielectric constant of about 2.3 is also being attempted.
Regarding the porosification of an insulating film, two methods have been reported. In one method, a film is deposited in such a way that a pore-forming material called a porogen is mixed into a backbone-forming material called a matrix, and then the porogen is removed only by heat treatment (refer to e.g. Japanese Patent Laid-open No. 2004-235548). In the other method, the porogen is removed by electron beam irradiation and heat treatment (refer to e.g. Japanese Patent Laid-open No. 2002-334873).